|
Author |
Message |
|
VP
Joined: 30 Jun 2008
Posts: 1050
Followers: 8
Kudos [?]:
214
[1] , given: 1
|
1
This post received
KUDOS
Which of the following sets has the same standard deviation as set (a, b, c)? (C) 2008 GMAT Club - m11#9 * (ab, b^2, cb) * (2a, b + a, c + b) * (0, b + a, c - a) * (ab, bc, ac) * (ab + c, a(1 + b), b(1+a)) Source: GMAT Club Tests - hardest GMAT questions http://gmatclub.com/tests/m11#expl9I think the explanation is missing/incomplete. Please help me through this problem.
_________________
"You have to find it. No one else can find it for you." - Bjorn Borg
Check out my GMAT blog - GMAT Tips and Strategies
|
|
|
|
|
|
|
|
|
SVP
Joined: 17 Jun 2008
Posts: 1593
Followers: 7
Kudos [?]:
131
[13] , given: 0
|
Re: m11#9 Official Explanation is incomplete ?? [#permalink]
 01 Nov 2008, 11:51
13
This post received
KUDOS
The standard deviation of a set does not change if a constant is added to all the members.
Thus, standard deviation of (a,b,c) will be the same as of (a+ab, b+ab, c+ab).
And, option E is the same as (a+ab, b+ab, c+ab).
|
|
|
|
|
|
GMAT Club team member
Joined: 02 Sep 2009
Posts: 11534
Followers: 1795
Kudos [?]:
9564
[1] , given: 826
|
1
This post received
KUDOS
amitdgr wrote: Which of the following sets has the same standard deviation as set (a, b, c)? (C) 2008 GMAT Club - m11#9 * (ab, b^2, cb) * (2a, b + a, c + b) * (0, b + a, c - a) * (ab, bc, ac) * (ab + c, a(1 + b), b(1+a)) Source: GMAT Club Tests - hardest GMAT questions http://gmatclub.com/tests/m11#expl9I think the explanation is missing/incomplete. Please help me through this problem. A. {ab, b^2, cb} B. {2a, b + a, c + b} C. {0, b + a, c - a} D. {ab, bc, ac} E. {ab + c, a(1 + b), b(1+a)} If we add or subtract a constant to each term in a set the standard deviation will not change.Notice that set {(ab + c, a(1 + b), b(1+a)}={c+ab, a+ab, b+ab}, so this set is obtained by adding some number ab to each term of set {a, b, c}, which means that those sets must have the same standard deviation. Answer: E.
_________________
PLEASE READ AND FOLLOW: 11 Rules for Posting!!!
RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory
COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!!
DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!
What are GMAT Club Tests?
25 extra-hard Quant Tests
Find out what's new at GMAT Club - latest features and updates
|
|
|
|
|
|
CEO
Joined: 29 Aug 2007
Posts: 2530
Followers: 41
Kudos [?]:
358
[0], given: 19
|
Re: m11#9 Official Explanation is incomplete ?? [#permalink]
01 Nov 2008, 12:53
scthakur wrote: The standard deviation of a set does not change if a constant is added to all the members.
Thus, standard deviation of (a,b,c) will be the same as of (a+ab, b+ab, c+ab).
And, option E is the same as (a+ab, b+ab, c+ab). Beautiful approach by scthakur. Thats the best approach to this question. +1. SD of a, b and c and (a+x), (b+x) and (c + x) is the same. Trying to find exactly what is the SD of a, b and c and the same of each of the options in the question doesnot help solve this question. What helps is understanding the question.
_________________
Verbal: new-to-the-verbal-forum-please-read-this-first-77546.html
Math: new-to-the-math-forum-please-read-this-first-77764.html
Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html
GT
|
|
|
|
|
|
CIO
Joined: 02 Oct 2007
Posts: 1261
Followers: 75
Kudos [?]:
506
[0], given: 334
|
Re: m11#9 Official Explanation is incomplete ?? [#permalink]
03 Nov 2008, 08:51
Yes, the part of the Official Explanation is missing. We'll edit it asap. +1. amitdgr wrote: Which of the following sets has the same standard deviation as set (a, b, c)? (C) 2008 GMAT Club - m11#9 * (ab, b^2, cb) * (2a, b + a, c + b) * (0, b + a, c - a) * (ab, bc, ac) * (ab + c, a(1 + b), b(1+a)) http://gmatclub.com/tests/m11#expl9I think the explanation is missing/incomplete. Please help me through this problem. _________________
Welcome to GMAT Club! 
   
Want to solve GMAT questions on the go? GMAT Club iPhone app will help.
Please read this before posting in GMAT Club Tests forum
Result correlation between real GMAT and GMAT Club Tests
Are GMAT Club Test sets ordered in any way?
Take 15 free tests with questions from GMAT Club, Knewton, Manhattan GMAT, and Veritas.
Find out what's new at GMAT Club - latest features and updates
|
|
|
|
|
|
Manager
Joined: 04 Dec 2009
Posts: 76
Location: INDIA
Followers: 2
Kudos [?]:
6
[0], given: 4
|
ans : E but approach of scthakur is great i got the ans by plug-in which take time thanks dear
_________________
MBA (Mind , Body and Attitude )
|
|
|
|
|
|
Intern
Joined: 18 Nov 2009
Posts: 24
Location: India
Schools: All options are open
Followers: 1
Kudos [?]:
3
[0], given: 1
|
I also agree with E for the same reason as mentioned above
|
|
|
|
|
|
Joined: 31 Dec 1969
Location: United States
Concentration: Marketing, Other
GMAT 1: 710 Q49 V38
WE: Accounting (Accounting)
Followers: 0
Kudos [?]:
32
[0], given: 54256
|
My approach was actually using real numbers such as a=2, b=3 and c=4. Though abit lengthy it worked since I applied the rule, the less spread out my answers were the closer my answer was making it E. Thanx now I know another rule;The standard deviation of a set does not change if a constant is added to all the members.
|
|
|
|
|
|
Intern
Joined: 28 Jul 2010
Posts: 10
Followers: 0
Kudos [?]:
1
[0], given: 1
|
E, addition or subtraction of Same constant term does not change standard deviation of the numbers
|
|
|
|
|
|
Manager
Joined: 21 Nov 2010
Posts: 141
Followers: 0
Kudos [?]:
2
[0], given: 12
|
Standard Deviation is the spread of numbers. question is asking which spread of letters equals a, b, c.
I picked numbers 2, 4, 6 for a, b, c.
Plugged in to find another set that has the same SD of 2. E is the only one that worked.
------
Please give me kudos if my post helps you.
|
|
|
|
|
|
Manager
Joined: 13 Feb 2012
Posts: 149
Location: Italy
Concentration: General Management, Entrepreneurship
GMAT 1: 560 Q36 V34
GPA: 3.1
WE: Sales (Transportation)
Followers: 4
Kudos [?]:
-1
[0], given: 85
|
Plugging numbers in it's not so time wasting, even though it is prone to errors. I put a=1, b=2, c=3 with a S.D of +/- 1 A = 2,4,6 B = 2,3,5 C = 0,3,2 D = 2,6,3 E = 5,3,4 E is the only set that has its numbers spread one integer apart.
_________________
"The Burnout" - My Debrief
Kudos if I helped you 
Andy
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
close
